Korn Shell Programming by Example

Arithmetic Expansion

Command substitution uses the expression $(...), where the output of what is inside the parentheses replaces the expression. Arithmetic expansion uses a similar expression: $(( ... )).

An easy example demonstrates this. The following is a simple program for performing arithmetic expansion:

#!/bin/ksh
a=5
b=6
c=$(( a*b ))
echo "$a * $b equals $c"

At first glance, the reader is probably unsure what will happen with the echo command. Here is the output of the script (named Example55.ksh):

$ ./Example55.ksh
5 * 6 equals 30

Notice that the echo command does not expand the math, but gives it literally. A common error here is in removing the double quotes from around the echo command. Here is the program without the double quotes: ...